The strength, deformation, and hydraulic properties of geomaterials, which constitute embankments, vary with fine fraction content. Therefore, numerous research studies have been conducted regarding the effects of fine fraction content on the engineering properties of geomaterials. Howe ver, there have only been a few studies in which the effects of fine fraction content on the soil skeletal structure have been quantitatively evaluated and related to compaction and mechanical properties. In this study, mechanical tests were conducted on geomaterials with various fine fraction contents to evaluate their compaction and mechanical properties focusing on the soil skeletal structure and void distribution. Furthermore, an internal structural analysis of specimens using X-ray computed tomography (CT) images was conducted to interpret the results of mechanical tests. As a result, it was discovered that the uniaxial compressive strength increased with fine fraction content, and the maximum uniaxial compressive strength was observed at a low water content, not at the optimum water content. Additionally, the obtained CT images revealed that large voids, which could ser ve as weak points for maintaining strength, decreased in volume, and small voids were evenly distributed within the specimens, resulting in a more stable soil skeletal structure.

The complex multiphase composition of frozen soil induces significant coupling interactions between the thermal, hydrological, mechanical, and damage fields during deformation, particularly under dynamic loading conditions. This study presents a hybrid decomposition phase-field model to investigate the multi-field coupling behavior and damage mechanisms of frozen soil. Unlike the spectral decomposition model, the proposed framework integrates isotropic degradation and the spectral decomposition methods, thereby enabling the simulation of damage evolution under compressive-dominated loading conditions. The model incorporates the viscous effects and strain rate sensitivity to accurately capture the dynamic response of frozen soil and establishes governing equations for coupled displacement, temperature, and fluid pressure fields. The applicability of the model was validated through confined compression experiments on frozen soil, demonstrating its capability to predict distinctive damage features, such as compaction bands oriented perpendicular to the loading direction, which represent the competitive interaction between the softening mechanism of pore collapse and the hardening mechanism of microstructural densification. This study provides significant advancements in the theoretical understanding and numerical simulation of the dynamic mechanical behavior of frozen soil.

This work proposes a novel plastic damage model to capture the post elastic flow-controlled damages in pavement-soil systems prescribed by the vibrations of moving load. Initially, the pavement structure has been modelled as a single-layer system resting on a spring-dashpot system representing soil mass. Then, multilayer modelling was adopted to analyze the post-elastic dynamic response in supporting plastic flow-controlled layers of geomaterial. Three mechanistic zones namely, elastic recoverable, transition, and post elastic zone have been conceptualized to identify the damage. The nonlinearity in stress and equivalent plastic strain has been observed for the set of selected velocities and load intensities specified in codal provisions. The variation in equivalent plastic strain is observed in the range of 10-16 to 10-3% in the granular base layer and 10-16 to 10-4% in the subgrade soil layer. The findings show that the equivalent plastic strain due to plastic flow prescribed by the vibrations of moving action of vehicular load at varied velocities is one of the root causes of permanent deformations. The propagation of dynamic load vibrations from the uppermost layer of pavement induces the generation of stress waves within distinct sub-layers of geomaterial. Hence, the observed behaviour leads to the generation of nonlinear stress waves prescribed by a vibrational mechanism of stress transfer (VMST). Therefore, the evaluation of the nonlinearities causing damage in pavement structure supported by flow controlled geomaterials has the potential to predict permanent deformations and its implications in the design of pavements supporting the transportation network.

More attention has been paid to integrating existing knowledge with data to understand the complex mechanical behaviour of geomaterials, but it incurs scepticism and criticism on its generalizability and robustness. Moreover, a common mistake in current data-driven modelling frameworks is that history internal state variables and stress are known upfront and taken as inputs, which violates reality, overestimates model accuracy and cannot be applied to modelling experimental data. To bypass these limitations, thermodynamically consistent hierarchical learning (t-PiNet) with iterative computation is tailored for identifying constitutive relations with applications to geomaterials. This hierarchical structure includes a recurrent neural network to identify internal state variables, followed by using a feedforward neural network to predict Helmholtz free energy, which can further derive dissipated energy and stress. The thermodynamic consistency of t-PiNet is comprehensively validated on the synthetic data generated by von Mises and modified Cam-clay models. Subsequently, the potential of t-PiNet in practice is confirmed by applying it to experiments on kaolin clay. The results indicate neural networks embedded by thermodynamics perform better on the loading space beyond the training data compared with the conventional pure neural network-based modelling method. t-PiNet not only offers a way to identify the mechanical behaviour of materials from experiments but also ensures it is further integrated with numerical methods for simulating engineering-scale problems.

In geotechnical engineering, bioinspired ideas such as snakeskin-inspired solutions for frictionally anisotropic continuum materials have been receiving increased attention due to their ability to create resilient and efficient geomaterial-continuum interfaces. Several studies have found that snakeskin-inspired continuum surfaces mobilise significant frictional anisotropy with different soils. However, studies on the effect of snakeskin-inspired patterns on other continuum geomaterials, such as rock surfaces, which can have promising applications like friction rock bolts, are rare. This study aims to address this gap by investigating the effect of snakeskin-inspired patterns on the shear behaviour of soft rocks, which is simulated by Plaster of Paris (PoP). For this purpose, snakeskin-inspired continuum surfaces with surface patterns inspired from the ventral scales of a snake with five different scale angles (10 degrees, 13 degrees, 16 degrees, 19 degrees and 22 degrees) were 3D printed with Polylactic Acid (PLA) polymer using a Fused Filament Fabrication (FFF) 3D printer. The interface shear behaviour of these surfaces with PoP was investigated using a customised interface shear testing apparatus under three normal loads: 1000 N, 2000 N and 3000 N. The results of the tests confirm that snakeskin-inspired patterns on continuum material mobilise substantial anisotropic friction and that the interface shear response depends on the shearing direction and the scale angle. The shearing direction significantly affects the peak and post-peak shear behaviour and the strain softening behaviour of the snakeskin-inspired interfaces. The study yields promising results for applying snakeskin-inspired patterns to create rock bolts with direction-dependent friction and enhances the existing knowledge in bioinspired geotechnics.

Micaceous residual soil (MRS), a marginal geomaterial commonly found in tropical regions, is often used in lowgrade construction projects due to budget constraints. However, little is currently known about its geotechnical properties, especially its long-term environmental response and microstructural variations. Investigated here is how mica content and climate-induced wetting-drying (WD) cycles affect the physical and mechanical properties of MRS. Reconstituted MRS samples with varying mica contents were prepared by mixing muscovite powder with plain residual soil, from which the original mica was removed. These samples were subjected to WD cycles to simulate tropical climate conditions. Geotechnical properties and microstructural changes were analyzed through systematic experimental tests and microscopic observations. The degradation observed during the WD cycles included crack propagation, volumetric swelling, reduced strength, and increased disintegration, all of which were positively correlated with mica content. Notably, for MRS with high mica content, the WD cycles ameliorated the soil brittleness, altering previous perceptions of uniformly low performance for MRS. The effect of mica on MRS under long-term environmental changes is attributed to both the inherent properties of mica and the particle packing structure in the soil. This study enhances the understanding of MRS behavior in tropical climate and provides technical recommendations for further improvement and effective application of this marginal geomaterial.

Soil-rubber mixtures have been proposed as cost-effective seismic and dynamic risk mitigation techniques. The granulated rubber used for these mixtures is obtained from end-of-life tires, allowing for stockpiles of waste rubber tires to be recycled. To date, most of the research has focused on the mechanical properties of sand-rubber mixtures, while limited studies have been performed on gravel-rubber mixtures (GRMs). In particular, GRMs with well-graded gravel (wgGRMs), which are of significant practical interest due to their availability, have only been poorly characterised. As part of a wider investigation aimed at facilitating the use of wgGRMs as geotechnical dynamic isolation systems, this paper presents bender element and small-strain cyclic triaxial test results performed on mixtures with 25%, 40%, and 55% volumetric rubber content. It is found that, thanks to their excellent energy absorption properties, wgGRMs can be efficiently adopted as geotechnical dynamic isolation to mitigate seismic risk of and anthropically induced vibrations on existing and new structures/infrastructures. Their easy implementation, low-cost, and widespread availability further facilitate their use.

In cold regions, the frozen soil-rock mixture (FSRM) is subjected to cyclic loading coupled with freeze-thaw cycles due to seismic loading and ambient temperature changes. In this study, in order to investigate the dynamic mechanical response of FSRM, a series of cyclic cryo-triaxial tests were performed at a temperature of -10 degrees C on FRSM with different coarse-grained contents under different loading conditions after freeze-thaw cycles. The experimental results show that the coarse-grained contents and freeze-thaw cycles have a significant influence on the deformation properties of FSRM under cyclic loading. Correspondingly, a novel binary-medium-based multiscale constitutive model is firstly proposed to describe the dynamic elastoplastic deformation of FSRM based on the coupling theoretical framework of breakage mechanics for geomaterials and homogenization theory. Considering the multiscale heterogeneities, ice-cementation differences, and the breakage process of FSRM under external loading, the relationship between the microscale compositions, the mesoscale deformation mechanism (including cementation breakage and frictional sliding), and the macroscopic mechanical response of the frozen soil is first established by two steps of homogenization on the proposed model. Meanwhile, a mixed hardening rule that combines the isotropic hardening rule and kinematic hardening is employed to properly evaluate the cyclic plastic behavior of FSRM. Finally, comparisons between the predicted results and experimental results show that the proposed multiscale model can simultaneously capture the main feature of stress-strain (nonlinearity, hysteresis, and plastic strain accumulation) and volumetric strain (contraction and dilatancy) of the studied material under cyclic loading.

In cold regions, the soil temperature gradient and depth of frost penetration can significantly affect roadway performance because of frost heave and thaw settlement of the subgrade soils. The severity of the damage depends on the soil index properties, temperature, and availability of water. While nominal expansion occurs with the phase change from pore water to ice, heaving is derived primarily from a continuous flow of water from the vadose zone to growing ice lenses. The temperature gradient within the soil influences water migration toward the freezing front, where ice nucleates, coalesces into lenses, and grows. This study evaluates the frost heave potential of frost-susceptible soils from Iowa (IA-PC) and North Carolina (NC-BO) under different temperature gradients. One-dimensional frost heave tests were conducted with a free water supply under three different temperature gradients of 0.26 degrees C/cm, 0.52 degrees C/cm, and 0.78 degrees C/cm. Time-dependent measurements of frost penetration, water intake, and frost heave were carried out. Results of the study suggested that frost heave and water intake are functions of the temperature gradient within the soil. A lower temperature gradient of 0.26 degrees C/cm leads to the maximum total heave of 18.28 mm (IA-PC) and 38.27 mm (NC-BO) for extended periods of freezing. The maximum frost penetration rate of 16.47 mm/hour was observed for a higher temperature gradient of 0.78 degrees C/cm and soil with higher thermal diffusivity of 0.684 mm(2)/s. The results of this study can be used to validate numerical models and develop engineered solutions that prevent frost damage.